Battery and electric bicycle

ABSTRACT

According to one embodiment, a battery includes: a first wire; a second wire; a third wire; a first resistor; a first switch; a second switch; a second resistor; a voltage measurer; and a controller that calculates a second resistance value of the third wire using a first voltage of a first battery when the first switch is turned on and the second switch is turned off, a second voltage of a second battery when the first switch is turned on and the second switch is turned off, a third voltage of the second battery when the first switch is turned off and the second switch is turned off, and a first resistance value of the first resistor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2016-020900 filed on Feb. 5, 2016, the contents of which are incorporated herein by reference in their entirety.

FIELD

Embodiments described herein relate generally to a battery and an electric bicycle.

BACKGROUND

A battery module has a configuration in which a plurality of secondary batteries are serially connected.

A battery measures voltages of the secondary batteries of the battery module and adjusts the voltages or amounts of charge.

In order to adjust a voltage or an amount of charge of a secondary battery, it is necessary to calculate a resistance value of a wire connected to the secondary battery in advance.

Some conventional methods of calculating a resistance value of a wire use voltages which are measured before and after a current flows in a circuit.

However, since a resistance value of an internal resistor of a battery is too small and is thus ignored, the resistance value of the internal resistor is not considered when calculating the resistance value of the wire.

Accordingly, in the conventional methods of calculating a resistance value of a wire, it is not possible to calculate an accurate resistance value of a wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a battery.

FIG. 2 is a diagram showing a process flow of a wire-resistance calculator.

FIG. 3 is a diagram showing a relationship between time and voltage of a secondary battery cell.

FIG. 4 is a diagram showing a relationship between time and voltage of a secondary battery cell.

FIG. 5 is a diagram showing a battery including a temperature measurer.

FIG. 6 is a diagram showing an electric bicycle including the battery.

DETAILED DESCRIPTION

According to one embodiment, a battery includes: a first battery that includes a first positive electrode and a first negative electrode; a second battery that includes a second positive electrode and a second negative electrode; a first wire that connects the first positive electrode and the second negative electrode; a second wire that connects the first negative electrode and the second positive electrode; a third wire that connects the first wire and the second wire; a first resistor that is inserted into the second wire between a junction point of the second wire and the third wire and the first negative electrode; a first switch that is inserted into the second wire between the first resistor and the first negative electrode; a second switch that is inserted into the second wire between the junction point and the second positive electrode; a second resistor that is inserted into the second wire between the second switch and the second positive electrode; a voltage measurer that measures a voltage between the first switch and the first negative electrode in the second wire, a voltage between the second resistor and the second positive electrode in the second wire, and a voltage of the junction point; and a controller, wherein the controller calculates a second resistance value of the third wire using a first voltage of the first battery when the first switch is turned on and the second switch is turned off, a second voltage of the second battery when the first switch is turned on and the second switch is turned off, a third voltage of the second battery when the first switch is turned off and the second switch is turned off, and a first resistance value of the first resistor.

Hereinafter, embodiments will be described with reference to the accompanying drawings.

Like elements will be provided with like reference signs.

The drawings are schematic or conceptual, and a relationship between a thickness and a width of each element, and sizes, specific coefficients, and the like of the elements cannot be said to be the same as they actually are.

The same element may be drawn with different sizes or specific coefficients in the drawings.

First Embodiment

FIG. 1 shows a configuration of a battery 10.

The battery 10 includes a secondary battery module 11, a voltage measurer 12, a power source 13, a current measurer 14, a cell balancing circuit 15, a cell balance controller 16, a storage 5, and a wire-resistance calculator 17.

The secondary battery module 11 includes n secondary battery cells 11-1, 11-2, . . . , and 11-n which are connected in series.

The secondary battery cells 11-1, 11-2, . . . , and 11-n are secondary batteries such as lithium ion batteries.

It is assumed that electromotive forces of the secondary battery cells 11-1, 11-2, . . . , and 11-n are defined as E_(l), E₂, , and E_(n), respectively, and internal resistors of the secondary battery cells 11-1, 11-2, . . . , and 11-n are defined as Ri₁, Ri₂, . . . , and Ri_(n), respectively.

The power source 13 is connected to a plus-side terminal and a minus-side terminal of the secondary battery module 11.

When the power source 13 is connected to the secondary battery module 11, the secondary battery module 11 is charged.

The power source 13 may be replaced with a load for use.

The load is a circuit or an element that consumes electric power.

When the load is connected to the secondary battery module 11, electric power of the secondary battery module 11 is consumed.

A voltage measuring line Lv₀ is a wire that connects a junction point T₀ and the voltage measurer 12.

A voltage measuring line Lv_(n+1) is a wire that connects a junction point T_(n+1) and the voltage measurer 12.

A voltage measuring line Lv₀₁ connects a junction point T₀₁ and the voltage measurer 12.

A voltage measuring line Lv₁₂ connects a junction point T₁₂ and the voltage measurer 12.

A voltage measuring line Lv₂₃ connects a junction point T₂₃ and the voltage measurer 12.

A voltage measuring line Lv_(n+1) connects a junction point T_(nn+1) and the voltage measurer 12.

The voltage measurer 12 measures a voltage between the plus-side terminal and the minus-side terminal of the secondary battery module 11.

The voltage measurer 12 measures a voltage between a positive electrode terminal and a negative electrode terminal of each of the secondary battery cells 11-1, 11-2, . . . , and 11-n.

A junction point S₀₁ of the voltage measuring line Lv₀₁ and a junction point S₁₂ of the voltage measuring line Lv₁₂ are connected.

A switch SW₁ and a resistor R₁ are inserted between the junction point S₀₁ of the voltage measuring line Lv₀₁ and the junction point S₁₂ of the voltage measuring line Lv₁₂.

The junction point S₁₂ of the voltage measuring line Lv₁₂ and a junction point S₂₃ of the voltage measuring line Lv₂₃ are connected.

A switch SW₂ and a resistor R₂ are inserted between the junction point S₁₂ of the voltage measuring line Lv₁₂ and the junction point S₂₃ of the voltage measuring line Lv₂₃.

A junction point S_(n−1n) of a voltage measuring line Lv_(n−1n) and a junction point S_(nn+1) of the voltage measuring line Lv_(nn+1) are connected.

A switch SW_(n) and a resistor R_(n) are inserted between the junction point S_(n−1n) of the voltage measuring line Lv_(n−1n) and the junction point S_(nn+1) of the voltage measuring line Lv_(nn+1).

The voltage measuring line Lv₀₁ between the junction point T₀₁ and the junction point S₀₁ includes a wire resistor Rl₀₁.

The voltage measuring line Lv₁₂ between the junction point T₁₂ and the junction point S₁₂ includes a wire resistor Rl₁₂.

The voltage measuring line Lv₂₃ between the junction point T₂₃ and the junction point S₂₃ includes a wire resistor Rl₂₃.

The voltage measuring line Lv_(nn+1) between the junction point T_(nn+1) and the junction point S_(nn+1) includes a wire resistor Rl_(nn+1).

The current measurer 14 is serially connected to the secondary battery module 11.

The current measurer 14 measures a current flowing in the secondary battery module 11.

The cell balance controller 16 controls switching of the switches SW₁, SW₂, . . . , and SW_(n).

For example, when the switch SW₁ is turned on, the secondary battery cell 11-1 is connected to the resistor R₁ and the secondary battery cell 11-1 is in a discharging state.

The wire-resistance calculator 17 calculates a resistance value of each of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1).

The storage 5 stores the voltage values of the secondary battery cells 11-1, 11-2, . . . , and 11-n measured by the voltage measurer 12, the current values measured by the current measurer 14, and the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , and Rl_(n−1n), and Rl_(nn+1) calculated by the wire-resistance calculator 17.

The cell balance controller 16 and the wire-resistance calculator 17 may be controlled by one controller (one circuit).

The cell balancing circuit 15 is a part including the secondary battery module 11, the switches SW₁, SW₂, . . . , and SW_(n), and the resistors R₁, R₂, . . . , and R_(n).

The cell balancing circuit 15 is a circuit that equalizes the voltages of the secondary battery cells 11-1, 11-2, . . . , and 11-n with each other.

The cell balancing circuit 15 is not particularly limited as long as it can individually charge and discharge one or more secondary battery cells.

Here, arrangement of parts will be described with a focus on the secondary battery cell (a first battery) 11-1 and the secondary battery cell (a second battery) 11-2 among the secondary battery cells 11-1, 11-2, . . . , and 11-n.

The positive electrode (a first positive electrode) of the secondary battery cell 11-1 and the negative electrode (a second negative electrode) of the secondary battery cell 11-2 are connected by a wire (a first wire) 1.

The negative electrode (a first negative electrode) of the secondary battery cell 11-1 and the positive electrode (a second positive electrode) of the secondary battery cell 11-2 are connected by a wire (a second wire) 2.

A wire (a third wire) 3 connects the junction point T₁₂ of the wire 1 and the junction point S₁₂ of the wire 2.

In the wire 2, the resistor (a first resistor) R₁ is inserted in series between the junction point S₁₂ and the negative electrode (the first negative electrode) of the secondary battery cell 11-1.

In the wire 2, the switch (a first switch) SW₁ is inserted in series between the resistor (the first resistor) R₁ and the negative electrode (the first negative electrode) of the secondary battery cell 11-1.

In the wire 2, the switch (a second switch) SW₂ is inserted in series between the junction point S₁₂ and the positive electrode (the second positive electrode) of the secondary battery cell 11-2.

In the wire 2, the resistor (a second resistor) R2 is inserted in series between the switch (the second switch) SW₂ and the positive electrode (the second positive electrode) of the secondary battery cell 11-2.

The voltage measurer 12 measures a voltage between the resistor R₂ and the positive electrode (the second positive electrode) of the secondary battery cell 11-2 in the wire 2, a voltage between the switch SW₁ and the negative electrode (the first negative electrode) of the secondary battery cell 11-1 in the wire 2, and a voltage of the junction point S₁₂.

The voltages of the secondary battery cells 11-1, 11-2, . . . , and 11-n which are measured by the voltage measurer 12 are defined as v₁ (V), v₂ (V), . . . , and v_(n) (V).

The voltage of the secondary battery module 11 that is measured by the voltage measurer 12 is defined as v (V).

The voltage measuring line Lv₀ and the voltage measuring line Lv₀₁ may be formed as a single wire.

The voltage measuring line Lv_(n+1) and the voltage measuring line Lv_(nn+1) may be formed as a single wire.

The wire-resistance calculator 17 calculates the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) when the absolute value of the current measured by the current measurer 14 is sufficiently small, that is, when the secondary battery module 11 is neither charged nor discharged.

One of the switches SW₁ to SW_(n) is turned on every predetermined interval k, and the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) are calculated.

Here, k is a predetermined natural number and is preferably 1 or 2.

When k=1, the cell balance controller 16 turns on the switch SW₁.

When the switch SW₁ is turned on, the wire-resistance calculator 17 calculates the resistance values of the wire resistor Rl₀₁ and the wire resistor Rl₁₂.

The cell balance controller 16 turns off the switch SW₁ and then turns on the switch SW₂.

The wire-resistance calculator 17 calculates the resistance values of the wire resistor Rl₁₂ and the wire resistor Rl₂₃.

The resistance value of the wire resistor Rl₁₂ is calculated two times when the switch SW₁ is turned on and when the switch SW₂ is turned off.

The wire-resistance calculator 17 can improve calculation accuracy of the resistance value of the wire resistor Rl₁₂ by calculating an average of the resistance values of the wire resistor Rl₁₂.

When k=2, the cell balance controller 16 turns on the switch SW₁.

When the switch SW₁ is turned on, the wire-resistance calculator 17 calculates the resistance values of the wire resistor Rl₀₁ and the wire resistor Rl₁₂.

The cell balance controller 16 turns off the switch SW₁ and then turns on the switch SW3.

The wire-resistance calculator 17 calculates the resistance values of the wire resistor Rl₂₃ and the wire resistor Rl₃₄.

When k=2, the wire-resistance calculator 17 calculates the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) at least one time.

Since the number of switches SW₁, SW₂, . . . , and SW_(n) which are controlled by the cell balance controller 16 is smaller than that of when k=1, a time in which the wire-resistance calculator 17 calculates the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) is shorter.

When k>2, all of the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) cannot be calculated, and thus all of the resistance values of all of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) are calculated by interpolation.

For example, it is assumed that the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) are the same.

At this time, an average value of the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) which are calculated by the wire-resistance calculator 17 is set as the resistance values of all the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1).

FIG. 2 shows a process flow of the wire-resistance calculator 17.

The wire-resistance calculator 17 starts a process flow (Step 101).

The cell balance controller 16 turns off all switches (Step 102).

Here, j denotes the number of the switches SW₁, SW₂, . . . , and SW_(n) controlled by the cell balance controller 16, and j is any one of 1, 2, . . . , and n.

When j=1 (Step 104), the wire-resistance calculator 17 stores the voltage v of the secondary battery module 11, the voltage v₁ of the secondary battery cell 11-1, and the voltage v₂ of the secondary battery cell 11-2 which are measured by the voltage measurer 12 in the storage 5, and defines the voltages as V′, V₁′, and V₂′.

Since no current flows in the secondary battery module 11, the voltage V′ of the secondary battery module 11, the voltage V₁′ (a fifth voltage) of the secondary battery cell 11-1, and the voltage V₂′ (a third voltage) of the secondary battery cell 11-2 are the same as an electromotive force E₁+E₂+ . . . +E_(n) of the secondary battery module 11, the electromotive force E₁ of the secondary battery cell 11-1, and the electromotive force E₂ of the secondary battery cell 11-2, respectively, (Step 105).

When the cell balance controller 16 turns on the switch SW₁, a current flows in the secondary battery cell 11-1, the wire resistor Rl₀₁, the resistor R₁, and the wire resistor Rl₁₂ (Step 106).

The voltage measurer 12 stores the measured voltage v of the secondary battery module 11, the measured voltage v₁ of the secondary battery cell 11-1, and the measured voltage v₂ of the secondary battery cell 11-2 in the storage 5, and defines the voltages as the voltage V of the secondary battery module 11, the voltage (a first voltage) V₁ of the secondary battery cell 11-1, and the voltage (a second voltage) V₂ of the secondary battery cell 11-2 (Step 107).

The wire-resistance calculator 17 calculates the resistance value rl₀₁ of the wire resistor Rl₀₁ and the resistance value (a second resistance value) rl₁₂ of the wire resistor Rl₁₂ using the voltage V′ of the secondary battery module 11, the voltage V₁′ of the secondary battery cell 11-1, and the voltage V₂′ of the secondary battery cell 11-2 which are measured by the voltage measurer 12 when the switch SW₁ is turned off in Step 105 and the voltage V of the secondary battery module 11, the voltage V₁ of the secondary battery cell 11-1, the voltage V₂ of the secondary battery cell 11-2, and the resistance value (a first resistance value) of the resistor R₁ which are measured by the voltage measurer 12 when the switch SW₁ is turned on in Step 107, and stores the calculated resistance values in the storage 5 (Step 108).

The cell balance controller 16 turns off the switch SW₁ (Step 109).

It is checked whether j=n is established (Step 119).

When j=n is not established, j=j+k is set in Step 120 and it is checked whether j>n is established in Step 121.

When it is determined that j>n is not established in Step 121, the process flow is returned to Step 104.

When it is determined that j>n is established in Step 121, j=n is set in Step 122 and the process flow is returned to Step 104.

Here, a method of calculating the resistance value rl₀₁ of the wire resistor Rl₀₁ and the resistance value rl₁₂ of the wire resistor Rl₁₂ in Step 108 will be described below.

The voltage V of the secondary battery module 11, the voltage V₁ (the first voltage) of the secondary battery cell 11-1, and the voltage V₂ of the secondary battery cell 11-2 which are measured by the voltage measurer 12 when the switch SW₁ is turned on in Step 107 are expressed by Equation (1), Equation (2), and Equation (3). Equation (1) V=V′−(Ri ₁)×I ₁   (1) Equation (2) V ₁ =V ₁′−(Ri ₁ +Rl ₀₁ +Rl ₁₂)I ₁   (2) Equation (3) V ₂ =V ₂ ′+Rl ₁₂ ×I ₁   (3)

Here, when a current flowing in the resistor R₁ is defined as I₁, the current I₁ can be calculated by Equation (4) using the voltage v₁ of the secondary battery cell 11-1 and a known resistance value r₁ of the resistor R₁

$\begin{matrix} {{Equation}\mspace{14mu}(4)} & \; \\ {I_{1} = \frac{V_{1}}{r_{1}}} & (4) \end{matrix}$

Accordingly, by substituting Equation (1), Equation (3), and Equation (4) into Equation (2) and arranging the equation with respect to the wire resistor Rl₀₁, the resistance value rl₀₁ of the wire resistor Rl₀₁ can be calculated by Equation (5).

$\begin{matrix} {{Equation}\mspace{14mu}(5)} & \; \\ {{rl}_{01} = {\left( {V_{1}^{\prime} - V_{1} + V^{\prime} - V + V_{2}^{\prime} - V_{2}} \right)\frac{r_{1}}{V_{1}}}} & (5) \end{matrix}$

By substituting Equation (4) into Equation (3), the resistance value rl₁₂ of the wire resistor Rl₁₂ can be calculated by Equation (6).

$\begin{matrix} {{Equation}\mspace{14mu}(6)} & \; \\ {{rl}_{12} = {\left( {V_{2} - V_{2}^{\prime}} \right)\frac{r_{1}}{V_{1}}}} & (6) \end{matrix}$

When j=1 is not established (Step 104) and j=n is established (Step 110), the wire-resistance calculator 17 stores the voltage v of the secondary battery module 11, a voltage v_(n−1) of a secondary battery cell 11-n−1, and the voltage v_(n) of the secondary battery cell 11-n which are measured by the voltage measurer 12 in the storage 5, and defines the voltages as V′, V_(n−1)′, and V_(n)′.

Here, since no current flows in the secondary battery module 11, the voltage V′ of the secondary battery module 11, the voltage V_(n−1)′ of the secondary battery cell 11-n−1, and the voltage V_(n)′ of the secondary battery cell 11-n are the same as the electromotive forces E₁+E₂+ . . . +E_(n), E_(n−1), and E_(n) of the batteries (Step 111).

When the cell balance controller 16 turns on the switch SW_(n), a current In (>0) flows in the secondary battery cell 11-n, the wire resistor Rl_(n−1n), the resistor R_(n), and the wire resistor Rl_(nn+1) (Step 112).

The voltage measurer 12 measures the voltage v of the secondary battery module 11, the voltage v_(n−1) of the secondary battery cell 11-n−1, and the voltage v_(n) of the secondary battery cell 11-n, and defines the measured voltages as V, V_(n−1), and V_(n) (Step 113).

The wire-resistance calculator 17 calculates the resistance values rl_(n−1n) and rl_(nn−1) of the wire resistors Rl_(n−1n) and Rl_(nn+1) using the voltages V′, V_(n−1)′, and V_(n)′ stored in the storage 5 by the wire-resistance calculator 17 in Step 111 and the voltages V, V_(n−1), and V_(n) measured by the voltage measurer 12 in Step 113, and stores the calculated resistance values in the storage 5 (Step 114).

The cell balance controller 16 turns off the switch SW_(n) (Step 109).

It is checked whether j=n is established (Step 119).

Since j=n is established, the process flow moves to Step 123 and then ends.

The voltage v of the secondary battery module 11, the voltage V_(n) of the secondary battery cell 11-n−1, and the voltage V_(n−1) of the secondary battery cell 11-n which are measured in Step 113 are expressed by Equation (7), Equation (8), and Equation (9). Equation (7) V=V′−(Ri _(n))×I _(n)   (7) Equation (8) V _(n−1) =V ₂ ′+rl _(n−1n) I _(n)   (8) Equation (9) V _(n) =V _(n)′−(Ri _(n) +rl _(n−1n) +rl _(nn+1))I _(n)   (9)

When j=1 is not established (Step 104) and j=n is not established (Step 110), that is, when 1<j<n is established, the wire-resistance calculator 17 stores a voltage v_(j−1) of a secondary battery cell 11-j−1, a voltage v_(j) of a secondary battery cell 11-j, and a voltage v_(j+1) of a secondary battery cell 11-j+1 measured by the voltage measurer 12, and defines these voltages as V_(j−1)′, V_(j)′, and V_(j+1)′.

Here, since no current flows in the secondary battery module 11, V_(j−1)′, V_(j)′, and V_(j+1)′ are the same as an electromotive force E_(j−1) of the secondary battery cell 11-j−1, an electromotive force E_(j) of the secondary battery cell 11-j, and an electromotive force E_(j+1) of the secondary battery cell 11-j+1, respectively (Step 115).

The cell balance controller 16 turns on a switch SWj, and then a current Ij (>0) flows in the secondary battery cell 11-j, a wire resistor Rl_(j−1j), a resistor R_(j), and a wire resistor Rl_(jj+1) (Step 116).

The voltage measurer 12 measures the voltage v_(j−1) of the secondary battery cell 11-j−1, the voltage v_(j) of the secondary battery cell 11-j, and the voltage v_(j+1) of the secondary battery cell 11-j+1 (Step 117).

The wire-resistance calculator 17 calculates the resistance values of the wire resistor Rl_(j−1j) and the wire resistor Rl_(jj+1) using the voltage V_(j−1)′ of the secondary battery cell 11-j−1, the voltage V_(j)′ of the secondary battery cell 11-j, and the voltage V_(j+1)′ of the secondary battery cell 11-j+1 stored by the wire-resistance calculator 17 when all of the switches are turned off and the voltage V_(j−1) of the secondary battery cell 11-j−1, the voltage V_(j) of the secondary battery cell 11-j, and the voltage V_(j+1) of the secondary battery cell 11-j+1 which are measured by the voltage measurer 12 when the switch SWj is turned on (Step 118).

The cell balance controller 16 turns off the switch SWj (Step 109).

It is checked whether j=n is established (Step 119).

When j=n is not established, j=j+k is set in Step 120 and it is checked whether j>n is established in Step 121.

When it is determined that j>n is not established in Step 121, the process flow is returned to Step 104.

When it is determined that j>n is established in Step 121, j=n is set in Step 122 and the process flow is returned to Step 104.

A method of calculating the resistance values of the wire resistor Rl_(j−1j) and the wire resistor Rl_(jj−1) in Step 118 will be described below.

The voltage Vj−1 of the secondary battery cell 11-j−1, the voltage Vj of the secondary battery cell 11-j, and the voltage V_(j+1) of the secondary battery cell 11-j+1 which are measured by the voltage measurer 12 are expressed by Equation (10), Equation (11), and Equation (12). Equation (10) V _(j−1) =V _(j−1) ′+r _(j−1j) I _(j)   (10) Equation (11) V_(j)=r_(j)I_(j)   (11) Equation (12) V _(j+1)=(V _(j+1)′)+r _(jj+1) I _(j)   (12)

When a resistance value r_(j) of the resistor R_(j) is known, Equation (11) and Equation (12) are substituted into Equation (10) and resistance values r_(j−1j) and r_(jj+1) of the wire resistors Rl_(j−1j) and Rl_(jj+1) are calculated by Equation (13) and Equation (14).

$\begin{matrix} {{Equation}\mspace{14mu}(13)} & \; \\ {r_{j - {1j}} = {\left( {V_{j - 1} - V_{j - 1}^{\prime}} \right)\frac{r_{j}}{V_{j}}}} & (13) \\ {{Equation}\mspace{14mu}(14)} & \; \\ {r_{{jj} + 1} = {\left( {V_{j + 1} - V_{j + 1}^{\prime}} \right)\frac{r_{j}}{V_{j}}}} & (14) \end{matrix}$

A method of calculating the voltages of the secondary battery cells 11-1, 11-2, . . . , and 11-n using the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1) which are measured in FIG. 2 will be described below.

Under the control of the cell balance controller 16, all of the switches SW₁, SW₂, . . . , and SW_(n) are turned off.

At this time, the voltages of the secondary battery cells 11-1, 11-2, . . . , and 11-n which are measured by the voltage measurer 12 are defined as V₁′, V₂′, . . . , and V_(n)′, respectively.

Under the control of the cell balance controller 16, operating conditions of the switches SW₁, SW₂, . . . , and SW_(n) corresponding to the secondary battery cells 11-1, 11-2, . . . , and 11-n are determined.

For example, when the voltage V₁′ (the fifth voltage) of the secondary battery cell 11-1 is higher than a predetermined threshold voltage or is higher than the voltages of other secondary battery cells such as the secondary battery cell 11-2, it is determined that the switch SW₁ corresponding to the secondary battery cell 11-1 should be turned on.

This determination is performed on the voltages V₁′, V₂′, . . . , and V_(n)′ of the secondary battery cells 11-1, 11-2, . . . , and 11-n.

That is, when it is determined that a secondary battery cell 11-m (where m is any one of 1 to n) satisfies the operating condition, a switch SW_(m) corresponding to the secondary battery cell 11-m is turned on.

A cell voltage V_(m) of the secondary battery cell 11-m, in which the switch SW_(m) is turned on, is detected by the voltage measurer 12.

The wire-resistance calculator 17 calculates a current I_(m) flowing in a resistor R_(m) from the cell voltage V_(m) when the switch SW_(m) is turned on.

That is, the wire-resistance calculator 17 calculates the current value of the current I_(m) in the secondary battery cell 11-m, in which the switch SW_(m) is turned on, on the basis of the resistance value of the resistor R_(m).

For example, when the switch SW₁ of the secondary battery cell 11-1 is turned on, the current value of the current I₁ is calculated on the basis of the resistance value r₁ of the resistor R₁.

The current value of the current I₁ is calculated by “I₁=V₁/r₁.”

The wire-resistance calculator 17 calculates a voltage drop value ΔV_(m) which is generated in a wire resistor Rl_(m−1m) and a wire resistor Rl_(mm+1) on the basis of the current value of the current I_(m).

The voltage drop value ΔV_(m) is calculated by “ΔV_(m)=I_(m)×(rl_(m−1m)+rl_(mm +1)).”

For example, when the switch SW₁ of the secondary battery cell 11-1 is turned on, the voltage drop value ΔV₁ which is generated by the resistance value rl₀₁ of the wire resistor Rl₀₁ and the resistance value rl₁₂ of the wire resistor Rl₁₂ is calculated on the basis of the current value of the current I₁.

The voltage drop value ΔV₁ is calculated by “ΔV₁=I₁×(rl₀₁+rl₁₂).”

The wire-resistance calculator 17 corrects the voltage V_(m) of the secondary battery cell 11-m by adding the voltage drop value ΔV_(m) to the voltage V_(m) of the secondary battery cell 11-m.

A true voltage of the secondary battery cell 11-m can be calculated by “V_(m)+ΔV_(m).”

For example, when the switch SW₁ of the secondary battery cell 11-1 is turned on, a true voltage (a fourth voltage) of the secondary battery cell 11-1 is calculated by adding the voltage drop value ΔV₁ to the voltage V₁ of the secondary battery cell 11-1 detected by the voltage measurer 12 (V₁+ΔV₁).

j=1 is set in Step 103 and it is checked whether j=n is established in Step 119, but this checking may not necessarily be performed.

For example, when the resistance value of the wire resistor Rl₂₃ is set as j=2 in Step 103. it is checked whether j=2 is established in Step 119.

Similarly, Step 103, Step 119, or the predetermined k may be changed depending on the resistance value of the wire resistor Rl_(jj+1) which will be calculated.

Since resistors of wires between a certain secondary battery cell 11-x and junction points T_(x−1x) and T_(xx+1) can be considered as an internal resistor Ri_(x) of the secondary battery cell 11-x, the resistor of the wire between the secondary battery cell 11-x and the junction point T_(x−1x) and the resistor of the wire between the secondary battery cell 11-x and the junction point T_(xx+1) do not have to be considered.

Since a small current flows in the wires between the junction points S₀₁, S₁₂, . . . , and S_(nn+1) and the voltage measurer 12 for the purpose of accurate voltage measurement, the wire resistors may be ignored.

Step 105, Step 111, and Step 115 may be performed after Step 109.

FIG. 3 is a diagram showing the voltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2 which are measured by the voltage measurer 12 when the switch SW₁ is turned on or off in the process flow shown in FIG. 2.

The horizontal axis represents time (seconds) and the vertical axis represents voltage (V).

A solid line indicates the voltage v₁ of the secondary battery cell 11-1 and a broken line indicates the voltage v₂ of the secondary battery cell 11-2.

Between a time t₁ and a time t₂, the switch SW₁ is turned on.

When the switch SW₁ is turned on, a current flows in the secondary battery cell 11-1.

The voltage v₁ measured by the voltage measurer 12 at this time is not the electromotive force of the secondary battery cell 11-1.

As expressed by Equation (2), the voltage of the secondary battery cell 11-1, that is, the voltage between the junction point T₀₁ and the junction point T₁₂, which should be measured cannot be measured due to an influence of a voltage drop in the wire resistors Rl₀₁ and Rl₁₂, in addition to a voltage drop in the internal resistor Ri₁ of the secondary battery cell 11-1.

Between the time t₁ and the time t₂, the voltage v₁ greatly decreases.

When the switch SW₁ is turned on, no current flows in the secondary battery cell 11-2.

Since the voltage v₂ of the secondary battery cell 11-2 which is measured by the voltage measurer 12 is a voltage between the junction point S₁₂ and the junction point S₂₃, a voltage rise due to the wire resistor Rl₁₂ is added thereto as expressed by Equation (3), and the voltage increases to be more than it is before the time t₁ and after the time t₂.

Accordingly, the voltage measurer 12 does not accurately measure the voltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2.

FIG. 4 shows the voltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2 which are corrected using the resistance values of the wire resistors Rl₀₁, Rl₁₂, Rl_(n−1n), and Rl_(nn+1) calculated by the wire-resistance calculator 17.

The horizontal axis represents time (seconds) and the vertical axis represents voltage (V).

A solid line indicates the voltage v₁ of the secondary battery cell 11-1 and a broken line indicates the voltage v₂ of the secondary battery cell 11-2.

Between a time t₁ and a time t₂, the switch SW₁ is turned on.

Immediately after the switch SW₁ is turned on, the voltage v₁ of the secondary battery cell 11-1 drops due to the internal resistor Ri₁ of the battery.

This is because a voltage drop due to the wire resistor Rl₀₁ and the wire resistor Rl₁₂ is added to the voltage v₁ of the secondary battery cell 11-1 shown in FIG. 3.

Immediately after the switch SW₁ is turned on, the voltage v₂ of the secondary battery cell 11-2 does not vary.

This is because a voltage rise due to the wire resistor Rl₁₂ is subtracted from the voltage v₂ of the secondary battery cell 11-2 in FIG. 3.

It is possible to accurately calculate the voltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2 by correcting the voltage v₁ of the secondary battery cell 11-1 and the voltage v₂ of the secondary battery cell 11-2 which are measured by the voltage measurer 12 using the resistance values of the wire resistors Rl₀₁, Rl₁₂, . . . , Rl_(n−1n), and Rl_(nn+1).

The battery 10 is used for an electric bicycle 20 shown in FIG. 6.

Second Embodiment

FIG. 5 shows a configuration of the battery 10 including a temperature measurer 18.

The battery 10 shown in FIG. 5 further includes the temperature measurer 18 in addition to the components of the battery 10 shown in FIG. 1.

The same elements shown in FIG. 1 will be provided with the same reference signs, and a description thereof will not be repeated.

The temperature measurer 18 measures temperatures around the secondary battery module 11 or the resistors R₁, R₂, . . . , and R_(n).

Since the resistance value r_(j) of the resistor R_(j) depends on the temperature, the resistance value r_(j) varies depending on the temperature.

A table in which the temperature measured by the temperature measurer 18 and the resistance value r_(j) of the resistor R_(j) are correlated with each other is stored in the storage 5 in advance.

A relationship between the temperature and the resistance value r_(j) of the resistor R_(j) is considered by setting temperature as the horizontal axis and setting the resistance value r_(j) of the resistor R_(j) as the vertical axis.

When the temperature is defined as T, the relationship between the temperature T and the resistance value r_(j) of the resistor R_(j) is expressed by Equation (15). Equation (15) r _(j) =aT+b   (15)

Here, a denotes a slope and b denotes an intercept.

For example, a=0.04 and b=30 (Ω) are set.

For example, the wire-resistance calculator (a controller) 17 acquires the resistance value (a third resistance value) of the resistor R₁ (the first resistor) corresponding to the temperature measured by the temperature measurer 18 from the table stored in the storage 5.

The wire-resistance calculator (the controller) 17 calculates the resistance value (a fourth resistance value) of the wire (the third wire) 3 using the voltage V₁ (the first voltage) of the secondary battery cell 11-1 (the first battery), the voltage V₂ (the second voltage) of the secondary battery cell 11-2 (the second battery), the voltage V′₂ (the third voltage) of the secondary battery cell 11-2 (the second battery), and the resistance value (the third resistance value) of the resistor R₁ (the first resistor).

The battery 10 including the temperature measurer 18 is used for the electric bicycle 20 shown in FIG. 6.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. A battery comprising: a first battery that comprises a first positive electrode and a first negative electrode; a second battery that comprises a second positive electrode and a second negative electrode; a first wire that connects the first positive electrode and the second negative electrode; a second wire that connects the first negative electrode and the second positive electrode; a third wire that connects the first wire and the second wire; a first resistor that is inserted into the second wire between a junction point of the second wire and the third wire and the first negative electrode; a first switch that is inserted into the second wire between the first resistor and the first negative electrode; a second switch that is inserted into the second wire between the junction point and the second positive electrode; a second resistor that is inserted into the second wire between the second switch and the second positive electrode; a voltage measurer that measures a voltage between the first switch and the first negative electrode in the second wire, a voltage between the second resistor and the second positive electrode in the second wire, and a voltage of the junction point; and a controller, wherein the controller calculates a second resistance value of the third wire using a first voltage of the first battery when the first switch is turned on and the second switch is turned off, a second voltage of the second battery when the first switch is turned on and the second switch is turned off, a third voltage of the second battery when the first switch is turned off and the second switch is turned off, and a first resistance value of the first resistor.
 2. The battery according to claim 1, wherein the controller calculates a fourth voltage of the first battery using the second resistance value of the third wire, the first voltage of the first battery, and the first resistance value of the first resistor.
 3. The battery according to claim 1, wherein when the first switch is turned off and the second switch is turned off, the controller turns on the first switch when a fifth voltage of the first battery is higher than the third voltage of the second battery, and turns on the second switch when the third voltage of the second battery is higher than the fifth voltage of the first battery.
 4. The battery according to claim 1, further comprising: a temperature measurer that measures a temperature around the first resistor; and a storage that stores a table in which the temperature and a third resistance value of the first resistor are correlated with each other, wherein the controller calculates the third resistance value corresponding to the temperature measured by the temperature measurer from the table stored in the storage, and calculates a fourth resistance value of the third wire using the first voltage of the first battery, the second voltage of the second battery, the third voltage of the second battery, and the third resistance value of the first resistor.
 5. An electric bicycle comprising the battery according to claim
 1. 